This invention relates generally to apparatus for logging inclined boreholes and more specifically to apparatus which eases tubing or casing re-entry of a well logging instrument, perforating gun or the like, in deviated oil and gas boreholes.
It has become relatively common within the last few years to drill wells in search of oil and gas, and the like, with a portion of the bore deviating from the usual vertical orientation thereof. The deviation or inclination may extend over some considerable distance, sometimes returning to the usual vertical orientation. It is common in the preparation of such an inclined well to set casing or pipe in the upper section of the well, thereby extending into the deviated or inclined portion, while leaving the lower section of the well open to the earth formations.
The relatively horizontal angle of the deviated portion of the wellbore makes traversal of the borehole with a typical logging instrument or perforating gun extremely difficult. The angle will not permit the wireline conveyed instruments to be easily moved into the lower portion of the borehole. Further, when raising the logging instrument from within the borehole it is not uncommon for the wireline to drag against the lower side of the casing in deviated sections. Attempts to cause the logging instruments to traverse from the "open hole" section of the borehole into the upper tubing or casing can be thwarted because of the cablehead, which connects the logging cable to the logging instrument, coming into jammed contact with the lower end of the tubing or casing. Attempts to force the logging instrument to enter the tubing or casing by exerting pulling force on the cable can result in the cable "pulling out" or breaking off at the cablehead. When this occurs, the instrument can be lost within the borehole.
Accordingly, the present invention overcomes the deficiencies of the prior art by providing an apparatus which assists the well logging instrument in re-entry into subsurface well casing in deviated oil and gas boreholes.